Tuberculosis, caused by Mycobacterium tuberculosis, continues to be a worldwide public health problem. WHO estimates that over one third of the world's population, 1.7 billion people, are infected with M. tuberculosis. There are 8 million new cases and 3 million deaths from tuberculosis annually. In recent years, the incidence of tuberculosis has been increasing worldwide as patients with AIDS are highly susceptible to M. tuberculosis infections. Infection with conventional M. tuberculosis strains can effectively be cured with a combination of anti-tuberculosis drugs. Multidrug resistant (MDR-TB) strains have emerged in several countries with case fatality ranging from 4O-6O% in immunocompetent individuals and >8O% in immunocompromised individuals. Key to any successful control and eradication efforts will be the acquisition of basic knowledge regarding the genetics, biochemistry and physiology of M. tuberculosis cells. In the past few years, a number of systems have been developed that permit gene transfer in mycobacterial species. The focus of this proposal is to use these genetic systems in order to define mechanisms by which quinolone antibiotics interact with M. tuberculosis so as to build a knowledge base to design novel quinolones with anti-M. tuberculosis activities.